The Leyden jar
originated about 1746 through the work of Dutch
physicist Pieter van Musschenbroek of the
University of Leyden and Ewald Georg von Kleist of Pomerania, working
independently.

A Leyden jar consists of a glass jar with an outer
and inner metal coating covering the bottom and sides nearly to the
neck. A brass rod terminating in an external knob passes through a
wooden stopper and is connected to the inner coating by a loose chain.
When an electrical charge is applied to the external knob, positive and
negative charges accumulate from the two metal coatings respectively, but
they are unable to discharge due to the glass between them. The result
is that the charges will hold each other in equilibrium until a
discharge path is provided. Leyden jars were first used to store electricity
in experiments, and later as a condenser in early wireless equipment.

Examples of Leyden Jars from my collection:

12" Leyden Jar
c. 1885

Early gold leaf Leyden Jars
1st half 19th century

Battery of six Leyden Jars

"Franklin's Bells"
Late 18th Century

Leyden Jar with
Lane's Discharging Electrometer
1890

A Lane apparatus is a
Leyden Jar fitted with a calibrated spark gap. They were used primarily
in medical applications, in order to regulate the amount of voltage
applied to the patient.

Demonstration
Leyden Jar

This jar can
be separated into three parts: The outer metal can, the glass jar, and
the inner metal electrode. It was used to demonstrate that the charge in
a Leyden jar is held in the glass, not the metal.